Buffing drum



J. L. SMITH BUFFING DRUM Oct. 5, 1948.

3 Sheetsf-Sheet 1 Filed Jan. 25, 1946 INVENToR.

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Oct. 5, 1948. J. SMITH Filed Jan` 25. 1946 BUFFm-G DRUM 3 Sheets-Shea?l 2 50 v 136 126 14,2 A A@ I y AH1346" 5i I f j 55 j A97.- f

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BUFFING DRUM 5 Sheets-Sheet 3 Filed Jan. 25, 1946 INVENTR.

strength to Patented Oct. 5, 1948 UITED STATES BUFFING DRUM Joseph Leigh Smith, Glen Ellyn, Ill. Application January 25, 1946, Serial No. 643,300

10 Claims.

The subject of this invention is a bufling drum for holding emery cloth'.

In order to understand the relationship of applicants drum to the problems which it overcomes, a statement of existing commercial art will be helpful. The type of drum most commonly used today on applications where the drum has a diameter of four inches or less consists of a shaft having mounted thereon a cylindrical rubber core (solid or air-filled) of compressible characteristics disposed between two metal discs together with means for pressing the two metal discs toward each other against th'e opposite ends of the cylindrical rubber core so as to compress the core and expand it radially. Before tightening the discs against the core, a preformed sleeve of emery cloth is positioned around the rubber core and the clearance is `so little that when the core is expanded by tightening up the discs, the emery sleeve is held tightly in position. The cost of a sleeve is several times the cost of the strip emery cloth from which it is made. In use, this assembly performs well when the R. P.

placed on tools which turn 7,000 to 20,000 R. P. M.-tools which are very common today-the rubber core lacks sufficiently uniform tensile prevent the development of bulges in the rubber core due to centrifugal force. While these bulges are undesirable because they may impair the uniformity of the finishing, the most serious'objection to a bulge arises from the fact that it unbalances the drum so that the assembly pounds violently. It is not practical to vutilize this rubber core type of construction where the R.

P. M. exceeds what has become a comparatively low figure. This undesirable development 0f bulges has been reduced by providing the emery sleeves with a comparatively strong backer or innerliner. These sleeves are referred to as stiff back sleeves. l

In the case of drums having a diameter of four inches or more, that most commonly in use consists of a split drum or a solid drum having a split in its surface parallel to its axis, for which is provided a strip of emery cloth which has its ends clipped together like the points of joinder of the inwardly directed portion of the conventional heart-shape figure. The clipped together ends are inserted in the slot drum is a spindle to which' the ends are fastened. By means `of a key the spindle is pulled up tight and the emery cloth is drawn tightly around the drum. This form of drum can be operated at high speeds, but the construction for pulling up and on the inside of the YM. does not exceed 5,000. When these drums are Russia, an entirerailroad ber: rstly, users the ends of the emery cloth' requires so much space that commercially, drums having a radius of less than four inches are not available. This type of locking spindle does not lend itself to a reduction in size so as to fit within a one-half', oneor two-inch drum while still providing sufcient grip to hold and facility to interchange th'e ends of the emery cloth.

It is frequently desirable in the case of a metal drum to interpose a thin compressible surface such as felt between the drum and the emery cloth,

In the case of these -two types of emery cloth sleeves, it is diiiicult to pack them. The reason is that the life of the sleeve would be impaired if it were folded, the fold creating a cracked condition in the emery surface which with use quickly in reases. The result is that in the case of the closed type of sleeve, it is difficult to place more than half a dozen inside of one in order to ship. Stiff back sleeves cannot be nested at all. Five hundred stiff -backed sleeves one-inch in diameter and four inches wide occupy a cubic foot. In a recent shipment of these stiff backed sleeves'to freight box car was loaded with boxes containing the sleeves and the sleeves themselves did not weigh much over one ton. Shipping the same amount of emery cloth cut to proper width and length would have required one-tenth to one-twentieth of the space.

The foregoing indicates that the commercial emery cloth buffing eld is dominated by the emery cloth sleeve, one type being a true sleeve while th'e other type has the two ends clipped together for insertion in a, drum slot. The sleeve dominates the eld even though the strip emery cloth of equal area costs but a fth or sixth of a sleeve of equal area and even though the cost of shipping the emery strips is but a fraction of the cost of shipping the sleeves. It should be understood that the manufacturers of the sleeves buy the emery cloth in strip form.

The commercial advantages possessed by the sleeves over the strip emery lcloth are two in numcan interchangeably mount on a single olrui'n emery cloth' sleeves having a full grit range, whereas a user of drums for holding emery cloth strips must have several drums of a given diameter each intended to accomodate emery cloth strips having a limited grit range; and secondly, sleeves lend themselves to rapid interchangeability while being tightly held on the drum when in locked position, whereas existing drums lor drum designs firmly grasp the emery cloth only after considerable adjustment which Workmen frequently will not perform with cara These will be discussed in order.

Emery cloth is manufactured in a wide range of grits. Applicant is particularly interested. in emery cloth having a grit range from 50 to 259 because in the inishing of most steel, emery cloths having this grit range are used. The ngures identify the size of openings in the screens for the particles which are actually deposited on the cloth to form the emery cloth. The lower the number, the larger the particle, and this is what is important, the thicker the emery cloth. A 5G grit emery cloth is twice as thick as a 250 grit emery cloth. Each grinding job can bestand most rapidly be performed by a given emery cloth of a particular courseness or linen-ess. It is self-evident that in the case of sleeves, the thickness of the emery cloth is immaterial. The manufacturer o-f sleeves simply maintains his inside diameter, and this enables the workmen to use asingle drum for a sleeve of any emery .cloth grit. In the case of drums for strip emery cloth, however, the thickness of the emery cloth has thusfar made it impossible to provide a locking means in a single drum which will accommodate a wide range of emery .cloth thicknesses while locking the ends equally tightly, and what is very important, quickly. A workman can untig'hten a screw on a rubber drum, slip oiT a Worn sleeve and put on a new sleeve quickly. Any drum that requires fumbling with the free ends of a strip of emery cloth and the tightening of complicated end holding Vmeans with substantial likelihood of unequally tightening, cannot compete. Existing drums for strip -emery cloth have locking means designed ,to accommodate a given thickness of cloth. One designed Yto grip a 100- grit emery cloth may not .even engage a Z50-grit cloth. The result is .that one must have several drums of the same size or one Vdrum with a .plurality of interchangeable locking means in order to accommodate .a full range of emery cloth grits. 'Iliis fact has commercially killed several small drums having satisfactorily `fast locking means for a given thickness of cloth only. An industry will Amaintain a plurality of drums of different diameters, but rather than buy a plurality of the same ksize Adrums with diierent locking means, it will buy the more expensive sleeves.

The second reason has 'been partly touched upon, namely the rapid interchangeability of sleeves as compared with strip emery clot-h. A drum for holding .strip emery cloth is unsatisfac Itoryrii it does not hold the emery cloth evenly and tightly around the drum surface, or if .it requires time consuming manual adjustments in order to effect such a tight even holding of the emery cloth. What is Wanted is a locking means which moves from open to locked position bya single turning movement and which maintains itself :in-locked position without the aid of pawls, etc. Such a locking :means .is diiicult to devise because the emery :surface is outwardly directed on the drum and `the emery `surfaces face each other when brought inwardly of the drum and some proposed locking means therefor have engaged .a smooth surface in order `to. grip the ends ofthe strip-andsuch locking means do not lhold Well.

The rst object of this invention is to provide a small drum for emery cloth strips which may be operated atspeeds up to twenty thousand revolutions per minute.

A second object vofthis invention is to provide a locking means which `upon a single turn `of 4wide rangefof thickness.

the wrist first locks one end of the cloth and then grips the emery surface of the other end of the strip and by pulling it inwardly tightens it around the drum. A feature of this inven-y tion is a lock shoe which on a first partial turn of the locking means grips one end of the emery cloth strip, 'and a tension shoe which on further movement of the locking means in the same direotion rst grips the other end of the strip and then tightens the strip around the drum. Turning the wrist in one direction rst locks one end v of the strip, then the other, and then tightens the strip around the drum.

The third object of this invention is to provide a small drum which will accommodate strip without change of parts emery cloth having a is a desire to locate the of the drum so as to aid drum.

'Two embodiments of the principal invention are illustrated. The first has locking and vtension Vshoes of uni-form thickness and the second has locking and tension shoes Aof tapered 'thickness which act as a cam. There is also shown an adaptation of applicants preferred locking means to a drum having a diameter of fcur inches or more. It is necessary to provide an arbor axially of larger drums and consequently it is -necessary to locate applicants locking means. A third embodiment of the invention shows such relocation of the locking means in a larger drum.

The invention is illustrated in two sheets of drawings wherein:

Figures 1, 2 and' 3 are diagrammatic illustrations `of the end View of applicants drum illustrating how it functions;

Figure Ai is a transverse longitudinal section of a of. applicants invention;

'Figures 6 and 7 are schematic illustrations of a locking means movable in a straight line as contrasted to a rotating movement illustrated in the preferred form;

Figure 8 is a schematic illustration of a secondV emodiment of applicantis invention wherein the locking and tension shoes possess cam surfaces;

Figure 9 is an end view of a third embodiment of applicants invention illustrating adaptation of applicants locking means to a larger drum Whichvcarries lan arbor;

Figure 10 is a fourth Aembodiment of the invention showing a cylindrical rubber segment for replacing the coil springs; and

Figure 11 is a fifthembodiment of the invention showing the use ofshaped steel springs.

Continuing to refer to the drawings .and particularly to Figure l, a diagram, applicant's fundamental objective of locking one end and then on the same locking movement gripping the other end and pulling the strip tightly and evenly around the drum is attained by a locking shoe i, a lcam I2, a ,tension shoe M, all functioning in a-cylindrical recess `H3 ina drum I8, the surface 2ER of which is connected to the cylindrical recess fby a slot 22. The cam I2 is pivoted on an axis 24 which is approximately the axis of the drum l1:8, .there being permitted a radially directed displacement -to accommodate different thicknesses cf'emery cloth -to rbe explained hereinafter. When the cam is in the position shown in Figure 1, the lockingshoe IB *under pressure Yfrom a spring 26 provides an Opening 28 between its end 30 and locking means axially exact balancing of the `section and Figure v5a preferred embodiment `the'anija-cent,wall of the recess I6 into whichmay Ancillary to this objectv be readily slipped one end 32 of an emery cloth strip 34, The emery surface of the strip which provides a purchase between the cloth and a smooth steel surface is outwardly directed and hence is engaged by the surface 34 of the locking shoe l0.

Turning the cam l2 one hundred and fifty degrees, results, referring to Figure 2, in locking the shoe l0 against the end 28 of the emery strip 34 while concurrently permitting the tension shoe |4 to move inwardly under the influence of springs 36 and 38 but only for a limited distance because of control means not here shown. This leaves an opening 46 between the end 42 of the tension shoe I4 and the cam l2 into which may be readily inserted the other end 44 of the emery strip 34.

It will be observed that the emery surface engages the surface of the cam, whichk is the rotating surface, while the smooth under surface of the strip 34 engages the shoe. Further clockwise rotation of the cam results in the leading edge 46 of the cam l2 to engage the end 44 and squeeze it against the tension shoe |4. At this moment, both ends of the emery strip 34 are tightly held between the cam i2 and shoes l0 and |4 respectively, but the strip 34 is not drawn tightly around the drum. On the contrary it is loose, or at least no tighter than the workman can make it by pulling the strip around the drum manually. This is the practical limit of usefulness of the locking means of existing drums because these locking means are working against the smooth under surface of the emerystrip, which provides no purchase and hence will not tighten. l

Further clockwise motion of the cam I2 results in the under side of the end 44 slipping along the smooth surface of the tension shoe while the emery side engaging the rotating cam will not slip and has no alternative but to pull up the strip tightly around the drum, as illustrated in Figure 3. The emery surface on applicants drum is far smoother, i. e., more perfectly cylindrical, than can be obtained by a sleeve mounted on either a solid rubber core or a pneumatic core. As sleeve mounted drums are turned up to speeds exceeding 5,000 R. P. M., there develops a whistling which demonstrates variations of the emery grinding surface from the desirable cylindrical form, a sound absent when applicants drum is turned up to 20,000 R. P. M.

Diagrammatic drawings and the foregoing illustration best illustrate the means for locking the two ends of an emery strip in applicants drum and drawing the strip tightly around the drum by a single clockwise motion of the wrist, i

As thus far described, applicants drum and locking means is designed for a given thickness of emery cloth with a slight range in thickness. One major feature of applicants device is the automatic .adjustability of the locking means to a wide range of thicknesses together with simple manual means for further increasing the range. This function is attained by permitting the cam I2 to move laterally under the control of springs. Because the thickness of emery papers having a range of 50 to 250 grits is actually a variation of a fraction of an inch, this feature can best be explained by describing applicants preferred form of drum, giving exact dimensions of critical parts of the locking device.

Referring now to Figures 4 and 5, applicants drum consists of an aluminum member 50 having a drum proper portion 52 and a hub 54 formed integrally therewith. The drum 52 contains a cylindrical recess 56 and the hub is centrally which vintersect a plan that bisects the bored and threaded at '58. A shank 6U having a shoulder 62 and an externally threaded portion 64 is made of hardened steel tightly'seated in the hub 54. The portion `64 contains a cylindrical recess 66 which is referred to herein as the cam stud seat 66. The hub 54 is drilled and threaded at 68 and 1U and after the shank 60 has been tightly seated in the hub, openings 12 and 14 are drilled so that they will be in exact alignment with the threaded openings 68 and 10.

A came 16 having the cross-sectional configuration shown inFigureA has an axially extending stud 18 which has an outside diameter substantially less than the inside diameter of cam stud seat 66. The face y61 of this stud may be smooth or if additional gripping power is desired, it may be knurled. The shoulder of the cam 16 engages both the shank and the end wall of the cylindrical recess '56 so as to limit the penetration of the stud 18 into the cam stud seat 66. A raceway 82 in the stud 18 receives balls 84 and 86 which are adjustably urged inwardly by a spring and a pair of lockable set screws, such as 88, and 92. A keyway 94 is broached in the cam 16.

Referring now to Figure 4, the locking shoe 96 is a segment of a cylinder of uniform thickness and has an outside diameter slightly less than the diameter of the cylindrical recess 56. The length of the lock shoe 96 is coextensive with the length of the recess 56. Its upper outside edge may have a plurality of wales 91 to gripbetter the emery cloth. Along two spaced radial lines shoe 16 and contains it axis, are cut two holes, such as 68', in each of which is xedly mounted a lock shoe :pin l A pair of holes, suchV as |62, are cut in the drum member 52 so as to be in axial alignment with thelock shoe pins and in these holes are positioned expansion springs and set screws, such as |04 and |06. Thetension shoe |06 has a uniform thickness and has the same degree of curvatureas the lock shoe 65. Two holes, such as I6, laterally spaced in a line which bisects the shoe, are threaded to receive two tension shoe guide screws, such as ||2, each of which has a head ||4. Each guide screw l|2 is reciprocable in a hole ||6 in the drum member 52 and limits movement of the tension shoe |08 inwardly of the recess 56 to a short distance when the head ||4 engages the shoulder |8. Two sets of threaded holes, such as ||1 and H9, contain two sets of expansion springs adjustably controlled by set screws, such as |20, |22, |24 and .|26. rlhe angularity of the sets of holes, such as ||1 and H9, with respect to the axis of the hole I6 is not believed to be important other than that they should be approximately equal.

The drum member 52 contains two radial slots designated by the numbers |28 and |30. Slot |36 is cut for the purpose of assisting in balancing the drum-exact balance being obtained by adding or cutting away metal during a balancing test in a well-known manner. The slot |30 does not exist for the purpose of making it possible to feed in the ends |32 and v|34 of an emery strip |36. The ends |28 and |34 can be fed only through the slot |28. l

It is evident that the shoe and cam assembly will hold a position in the cylindrical recess which is a resultant of the forces exerted by the various springs in the drum member 52. It' is further evident that the cam 16 may move vertically by a distance at least equal to the clearance between the stud 18 and the caml stud seat 66. In a commercial embodiment wherein the Jcani stud seatis .265 inch, the cam :stud is .-235 inchso 'thfat the difference is .030 inch. In fact, aconsi'dera'bly :greater play is permitted the 'cam 'Miwhi'c'hv may rock :a little 'lengthwise during a tightening step. Thus, in the same commercial embodiment the circular .surface of the "cam has adiameter of .625 inch while the inside diameter of either shoe is .687 inch, a difference of .062, Moreover, the outside diameter of the shoes is slightly less than the diameter of the recess 56 so 'that there is little play here. The springs, such :as H14., located where .they are toward the lower side ofthe Aloch shoe 98 tend to thrust the shoe upwardly towardl the slot |28. Ii the paper is thick this movement is much more limited than when it -is thinner. It will ybe noted 'that the varying thicknesses of the emery cloth between the cam and the tension shoe are taken up by lt-he springs which may exert more or less pressure in accordance with the position of the set screws.

The crux of this invention lies in providing two surfaces on the interior of the drum, i. e., a locking lsurface l and a tension surface |42, which in the case of surface |42 is smooth so as to assist in movement of the smooth undersurface of the emery strip. While the surface |42 is on the :tension shoe |88 in this particular embodiment, it fcould be on the drum itself excepting for the desire to compensate for different thicknesses of emery cloth. In connection with these two surfaces, applicant uses an intermediate member such a's the shoe 95 which engages the rough emery surface of the cloth and the cam 'FS which engages both the locking shoe and the rough `emery surface of the other end of the cloth. It

is evident that the locking surface |118 instead of bein-g curved could be flat or there could just :be a single edge which was engaged by a member performing the function* of the shoe S6. Similarly., the tension surface |42 could be flat or some other configuration which, however, might Areduce the total area of thorough emery surface engaged by the locking means. In this respect, therefore, it is desirable that the inside curvature of the tension shoe |88 be approximately the 'same as the outside surface of the cam 78 so that the purchase obtained by the cam on the emery 1cloth increases as the emery cloth is drawn tightly .and tends more to pull fre By way of illustrating the basic principles of applicants locking device, diagrammatic views f5 and l are shown in the drawings. Referring to Figure 6, a shoe Hifi is movable horizontally toward and away from the surface |66 on the drum |48. A locking bar |59 is reciprocable vertically of Vthe slot l| 52 which has a tension surface T54. The tension surface |54 is separated from the Vwall |56 of the slot by a shoulder. When the bar |58 is .moved downwardly the lug |58 pushes the shoe .IM to the left so as to lock a pieceof -emery cloth. Further downward movement of the bar |58 so as to engage the other end |50 of emery cloth strip will rst lock it against the tension surface |54 and furthermovement will pull it on down. Figure 7 shows the same con-v struction With a locking bar |82 movable on a path at right angles to the principal axis of the slot. Theinvention disclosed in the major embodiment covers these two suggesteddevices,

Two other embodiments of the invention are shown in Figures 8 and 9. In the first embodiment, referring to Figure 8, the locking slice |68 has greater thickness at the end 82 than at the yend |64 and the tension shoe |86 has a greater thickness toward its lower end. rIhe vcam member |88 has 'an outside diameter slightly less than that on the inside of the shoes, the curvature in all cases being true arcs of a circle. By rot-ating the cam, the locking shoe is locked upwardly, While the tension shoe is locked outwardly an'd downwardly.

In the embodiment shown in Figure 9, the drum |71) has a central arbor |12. This arbor is required in the case of larger drums, that is, drums some four inches to two feet, because the tools upon which they are mounted carry some form of spindle. It is impossible, therefore, to mount the locking means coaxially of the drum. In the form illustrated in Figure 9, two of applicants locking means are shown balanced on opposite sides of the arbor.

Figures 10 and ll illustrate two embodiments of the invention which may become the successful commercial embodiments of the invention. Drilling the principal housing as illustrated in Figure 4, seating the pins in the shoes and assembling the ysaine with springs, constitutes a major element vof cost in the `embodiment first described. The-embodiments shown in Figures 10 and 1l seek to eliminate what is believed to be avoidable construction. In Figure 10, the shoe |88 has the same shape as the 4locking shoe in other embodiments but it is forced toward the locking area |82 by a compressible cylindrical segment |84 s0 as to perform the same function as the spring |84 in Figure 4. In order to prevent endwise displacement of the shoe, the cylindrical casting |85 has an annular channel therein into which the rubber pressure member |84 and the shoe |80 may be slipped. With respect to the tightening shoe, the rubber cylindrical segment |88' extends in valmost a 180 degree arc.

Referring to Figure 1l, the rubber cylindrical segments |84 and |88 of Figure 10 lhave been ree placed by spring members |90 and |92.

Having thusdescribed my invention, .what I claim as new and wish .to secure by Unit-ed States Letters Patent is:

1. A -bufin-g drum 4comprising a cylinder, Kan -arbor mounted axially on one side of said cylinder, `=a transverse passageway -diametrically through said cylinder, a cylindrical chamber 'axially positioned in said cylinder, a pair yof shoes each in the shape of a cylindrical segment and one positioned adjacent the chamber wall on one side of the passageway and the other positioned adjacent .the chamber wall on the other side of `the passageway, and a semi-cylindrical locking element axially positioned in the chamber and having its outer surface engageable with the inner surface of the lshoes.

2. A bu'ing drum comprising a cylinder, a pair of spaced, facing walls extending inwardly f-rom Ithe cylinder surface and parallel to the cyllnderfs axis, -a holding shoe Vmovable toward one of said walls, `ra flocking member movable toward the Yother wall, and means on the locking member for pressing the holding shoe against its wall as the locking member moves toward its 'associated Wall.

3. A lbuingdruin comprising a cylinder, a pair of spaced, facing wall-s extending inwardly from .the cylinder Isurface and parallel to 'the cylinders axis, a holding shoe movable toward one of 'said Walls, Ialock-i'ng member, a surface on the locking member directed toward the secon-d wall and complementary thereto for flush -engagement therewith and for sliding along said surface, Iand means on the locking member for pressing the holding shoe against its associated wall as the complementary surface of the locking member slideably engages its associated wall. I

4. A buing drum comprising a cylinder, a cylindrical chamber therein having an -axis parallel to the axis of said cylinder, a passageway having a rectangular cross section connecting the surface =of the cylinder to the cylindrical chamber, a holding shoe movable toward one wall of the chamber that extends parallel to the axis of the cylinder, an insert having a thickness substantially equal to th-at Iof -the shoe positioned against the wall 1of the chamber adjacent the opposite wall `of the passageway, and a rotata le member positioned substantially -coaxially of the chamber said rotatable member having a curving external surface concentric with 4the wall of the -chamber and having a radius s-uic-ient to press the holding shoe and the insert ltoward the walls of the chamber.

5. A bufiing drum comprising a cylinder, a cylindrical chamber coaxial-ly positioned therein, a slot connecting the cylinder's surface with said chamber, an axial-ly rotatable member `in said chamber 'having a surface consisting yof a segment of -a cylinder, and a pair lof shoes in the shape of cylindrical segments positioned between said rotatable member and the walls of said chamber.

6. A bufng drum comprising a cylinder, a

cylindrical chamber coaxially positioned therein,

a passageway having spaced, fac-ing Vwalls extending lengthwise of the cylinders axis and connecting the -cylinders surf-ace with said chamber, an axially rotatable member in said chamber having a surface consisting of a segment yof a cylinder, a pair of shoes in the shape of cylindrical segments positioned betwen said rotatable member Iand the walls of said chamber, and means engageable with each shoe for lpreventing rotative movement Iof the same.

c '7. A puffing drum comprising a cylinder, a cylindrical chamber -coaxially positioned therein, a passageway having spaced, facing walls extending lengthwise of the cylinders -axis and connecting the -cylinders surface with said chamber, an axially rotatable member in said chamber having a surface consisting of a segment of a cylinder, and a pair of shoes in the shape of cylindrical segments positioned between said rotatable member and the walls of said chamber, said shoes having their outer su'rfaces curved on a shorter radius than the wall `of the chamber and their inner surfaces curved on a greater radius than the surface -of the rotatable member.

Number 10 8. A buing drum comprising a cylinder, a cylindrical chamber therein having an axis parallel to the axis of the cylinder, a pasageway having spaced, facing walls extending lengthwise of 4the 5 cylinders Iaxis and connecting the -cylinders surface to said chamber, an axially lrotatable member in said chamber having a surface -consisting of a segment of a cylinder, and a pair yof shoes in the shape of cylindrical segments positioned between said rotatable member andthe walls of said chamber.

9. A bung drum compri-sing a cylinder, a cylindrical chamber therein having its axis parallel to the axis of the cylinder, a passageway having spaced, facing walls extending lengthwise of the Icyl-inders axis and connecting the cyliniders surface to said chamber, an axially rotatable member lin said recess having a surface consisting `of a segmentof a cylinder, a pair `of shoes ln 2o the shape of cylindrical segments oppositely disposed between said rotatable member and the wall-s of said recess so that one end of each shoe 'is adjacent to the passageway, and spring means urging both shoes toward the rotatable member.

19. A bumng drum comprising a cylinder, a cylindrical chamber coaxially positioned therein, a passageway having spaced, facing walls extending lengthwise of the cylinders axis and connecting the cylinders surf-ace to said chamber, an

CJI

axially rotatable member in said chamber having a surf-ace consisting `of a segment lof a cylinder, a pair yof shoes in the shape of cylindrical segments oppositely disposed between said rotatable member and the walls of said chamber so that one end of each shoe is adjacent to the-slot, land spring means urging b-oth shoes tow-ard the rotatable member.

. JOSEPH LEIGH SMITH.

REFERENCES CITED UNITED STATES PATENTS Name Date 603,357 Bagley May 3, 1898 986,246 Tone Mar. 7, 1911 1,374,052 Brauner Apr. 5,4 1921 2,119,279 Kerr et al May 31, 1938 A FOREIGN PATENTS Number Country Date 853,814 France Nov. 15, 1938 

